The use of wireless communication for in-home, in-building networks and point-to-point communications is increasing in popularity and spawning relatively new standards including, but not limited to Bluetooth, IEEE 802.11a, and IEEE 802.11b. As is known for wireless communications, data is modulated on to at least one radio frequency (RF) carrier frequency and transmitted as a RF modulated signal by a radio transmitter. A radio receiver receives the RF modulated signal and demodulates it to recapture the data.
As is further known, there are a variety of modulation/demodulation protocols that may be used for wireless communications. Such modulation/demodulation protocols include amplitude modulation (AM), frequency modulation (FM), amplitude shift-keying (ASK), frequency shift-keying (FSK), phase shift-keying (PSK), orthogonal frequency division multiplexing (OFDM), or variations thereof. As is also known, Bluetooth utilizes an FSK modulation/demodulation protocol, while IEEE 802.11a and IEEE 802.11b utilize OFDM and/or a form of PSK for its modulation/demodulation protocol.
Regardless of the particular modulation/demodulation protocol, a radio receiver generally includes an antenna section, a filtering section, a low noise amplifier, an intermediate frequency (IF) stage, and a demodulator. In operation, the antenna section receives RF modulated signals and provides them to the filtering section, which passes RF signals of interest to the low noise amplifier. The low noise amplifier amplifies the received RF signals of interest and provides them as amplified RF signals to the IF stage. The IF stage includes one or more local oscillators, one or more mixers, and one or more adders to step-down the frequency of the RF signals of interest to an intermediate frequency or to base-band. The IF stage provides the intermediate frequency signals or base-band signals to the demodulator, which, based on the demodulation protocol, recaptures the data.
A demodulator may be implemented using analog and/or digital circuitry. Digital demodulators are generally better suited for use in an integrated circuit (IC) radio receiver than analog demodulators because of reduced sensitivity to noise and less IC real estate intensive. Such demodulators typically require high order low pass filters and sophisticated DC offset correction circuitry.
Such high order low pass filters are typically required to pass the frequencies of interest and sharply attenuate other frequencies (e.g., at a rate of −60 dB/decade). To achieve such a large roll-off, digital high order low pass filters require a significant amount of logic circuits including multipliers.
For FSK demodulation, such as used in Bluetooth, the DC offset correction circuitry corrects for frequency differences between the local oscillations of IF stage in the transmitter section of a sending radio and in the receiver section of the receiving radio. Presently, such DC offset correction circuitry performs peak and valley detection to identify a peak and valley. From these values a DC value is determined (e.g., typically a midpoint between the peak and valley). The peak and valley values are continuously updated, thus the DC value is also continually updated. While this continuous updating allows for fast and continuous correction of the DC offset value, such circuitry is subject to false peak and/or valley detection. When a false peak or valley is detected, an error results in the DC value, which adversely affects the performance of a wireless radio.
Therefore, a need exists for a reliable, low cost, reduced complexity, and reduced integrated circuit real estate digital demodulator for use in integrated circuit radios and/or integrated circuit radio receivers.